Stable isotope enrichment, dietary sources and trophic overlap between silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis)

• We tested isotope fractionation and dietary sources for silver carp and bighead carp.
• Similar nitrogen isotope enrichment was recorded for the two fish.
• Trophic position estimates revealed partial dietary overlap.
• More natural diet was consumed by bighead carp than silver carp.

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) are important cultivated fish and their dietary sources have been subject to many studies. In the present work, stable isotope analysis (δ13C and δ15N) was used to assess the relative contributions of natural and artificial diets to the growth and dietary overlap in these fish. In an indoor growth experiment, the δ13C and δ15N values of muscle tissue of silver carp and bighead carp fed a fish meal as the sole protein source revealed identical isotope enrichment. In an outdoor growth experiment conducted in fishponds, the relative contribution of particulate organic matter (POM) and a commercial composite diet (CD) to the growth of both carps was estimated using a two-source isotope mixing model. Results revealed that bighead carp used more POM than silver carp for their growth. Estimates of dietary overlap between these fish suggest that silver carp and bighead carp partially shared the same diets for growth. This finding is consistent with the results of several recent studies, demonstrating that the trophic niche of these planktivores was not segregated, as was previously suggested.